Effects of Supplement Type and Feeding Frequency on Performance and Physiological Responses of Yearling Brahman-Crossbred Steers

The objective of this experiment was to investigate the effects of supplement type and feeding frequency on performance of yearling steers. Twenty-four steers were stratified by initial BW and randomly assigned to one of 3 treatments: 1) molasses-based supplement fed 3 times/wk (ML), 2) citrus pulp-based supplement fed 3 times/wk (C3), or 3) citrus pulp-based supplement fed daily (C7). Supplement intakes were formulated to be isocaloric and isonitrogenous. Limpograss hay was offered in amounts to ensure ad libitum intake. Steer shrunk BW was measured at the beginning and at the end of the experiment. Blood samples were collected for determination of plasma metabolites and hormones. Forage DMI was recorded daily during an 18-d period. Mean BW gain was greater

Key words: feeding frequency, performance, steers, supplement type


INTRODUCTION

Energy supplementation is essential for grazing beef cattle operations based on pastures of subtropical and tropical forages because these perennial grasses usually do not have adequate energy concentration to meet the requirements of growing cattle (Moore et al., 1991). The frequency at which supplements are offered depends on the supplement type and also on the management system of the operation. According to a review compiled by Kunkle et al. (1999), cattle supplemented daily, 3 times/wk, or once a week had similar rates of BW gain. However, the majority of these publications utilized protein or grain-based supplements, and none evaluated energy supplements based on low starch by-products such as molasses or citrus pulp.

Citrus pulp and molasses originate respectively from citrus and sugarcane industries. Molasses, despite its high DM content (approximately 75%), is classified as a liquid feed, whereas citrus pulp is commonly processed and fed as dry pellets. Differences in physical form between citrus pulp and molasses may lead to differences in intake behavior (Arthington et al., 2004). Molasses and citrus pulp also differ in their carbohydrate profile. Although both are low-starch energy feedstuffs, sucrose is the main carbohydrate of molasses (Pate, 1983), whereas pectin is the main carbohydrate of citrus pulp (Arthington et al., 2002). Pectin and sucrose are fermented differently in the rumen (NRC, 2001), which may impact forage intake, diet digestibility, energy utilization, and animal performance.

The objective of this experiment was to investigate the effects of supplement type and feeding frequency on performance, plasma metabolites, and hormones associated with energy intake, and voluntary forage intake of yearling steers.

MATERIALS AND METHODS

The experiment was conducted at the University of Florida - IF AS, Range Cattle Research and Education Center, Ona, during the months of November and December 2004. The animals utilized in this experiment were cared for by acceptable practices as outlined in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (PASS, 1999).

Animak and Diets

Twenty-four Brahman x British crossbred steers (BW ± SD = 257 ± 26 kg; age ± SD = 12 ± 1 mo) were utilized in this experiment. Steers were stratified by initial BW and randomly allocated to 12 pens (2 steers/pen). Pens were assigned randomly to 1 of 3 treatments (4 pens/treatment): 1) molasses-based supplement fed 3 times/wk (ML), 2) citrus pulp-based supplement fed 3 times/wk (C3), or 3) citrus pulp-based supplement fed daily (C7). Supplement intakes were formulated to be isocaloric, isonitrogenous, and balanced for Ca concentration (Table 1), given the high concentration of Ca in citrus pulp. Limpograss (Hemarthria altissima) hay (54% TDN and 9.1% CP; DM basis) was coarsely ground and offered at amounts to ensure ad libitum intake throughout the study. Steers also had free access to a complete commercial mineral-vitamin mix (14% Ca, 9% P, 24% NaCl, 0.20% K, 0.30% Mg, 0.20% S, 0.005% Co, 0.15% Cu, 0.02% I, 0.05% Mn, 0.004% Se, 0.3% Zn, 0.08% F, and 82 IU/g of vitamin A) and water.

Sampling

One week before the start and at the end of the study, steers were weighed for 2 consecutive days to determine both full and shrunk BW (after 16 h of feed restriction). Only shrunk BW values were utilized to calculate steer BW gain.

During the first 3 weeks of the study (d 1 to 21), blood samples were collected immediately prior and 4, 8, 24, 32, and 48 h after the first supplement feeding of the week (d 1, 8, and 15) for determination of glucose, BUN, insulin, IGF-I, and growth hormone (GH) concentrations.

For the second part of the study (d 22 to 40), forage DMI was recorded daily. Hay was offered in amounts to ensure ad libitum intake, and orts were collected and weighed daily. During this period, samples of the offered hay were collected twice (d 25 and 35) for determination of DM and nutrient composition, whereas samples of the non-consumed hay were collected daily from each pen to determine DM content. Hay samples were dried for 96 h at 50°C in forced-air ovens. A random sample of each feedstuff used in the study was collected at the beginning of the trial and analyzed for nutrient composition at commercial laboratories (Dairy One Forage Laboratory, Ithaca, NY, for hay, cottonseed meal, and citrus pulp samples; SDK Laboratories, Hutchinson, KS, for molasses samples).

by Cooke, R F, Arthington, J D, Staples, C R, Qiu, X
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